Sarcopenia, the age-related loss of muscle mass and strength, is a major health concern that contributes to the onset of frailty. Frailty and sarcopenia are major predictors of mortality, poor prognoses and loss of independence. Most importantly, the older adult with sarcopenia and/or frailty has a diminished quality of life. Identifying interventions that prevent, attenuate, and/or reverse the loss of muscle mass and strength will have a significant impact on improving the quality of life, both for basic activities of daily livig and recreational pursuits. The long-term goal of my research is to establish interventions for sarcopenia and frailty. The working hypothesis is that sarcopenia interventions will restore functional ability and extend healthspan. In preliminary work, using a cross-sectional cohort of mice to characterize age-related declines in functional and physiological ability, we developed a Neuromuscular Healthspan Scoring System to evaluate potential treatments. The next step is to test an intervention for sarcopenia. Resistance exercise is a well-accepted treatment for sarcopenia. Hence, the hypothesis for the proposed research is that resistance training will result in improved physical function, strength, and healthspan. This hypothesis will be tested with two Specific Aims: (1) Develop a resistance training model for mice and (2) Determine the effects of a resistance exercise training protocol on functional performance, muscle contractility, muscle remodeling and cellular mechanisms contributing to hypertrophy in adult, old, and aged mice. The main mechanisms to be examined include activation of the PI3k Akt mTORC1 pathway and satellite cell proliferation. The proposed studies use current technologies and approaches including mass spectrometry, single skeletal muscle fiber physiology, whole muscle physiology, and immunohistochemistry. Both mentors for this proposal, Drs. Thompson and Ferrington, are well-established scientists in the fields of aging, muscle, biochemistry and proteomics, have a strong history of successful mentorship, collaborations, funding and are well published. An advisory team, composed of experts in the fields of statistics, aging, proteomics, myogenic precursor cell biology, translational research and exercise physiology, will provide critical scientific guidance and career advice. The training program is tailored to meet my career goals by providing opportunities to enhance my scientific skill set, interact with established scientists, attend and present at national meetings, write and publish scientific papers, and mentor an undergraduate student. Lastly, the laboratories of my mentors and collaborators, the core facilities and Centers within the Medical School, and at the University of Minnesota will provide an exceptional environment for my training. I am firmly committed to studying aging in my career and will be seeking a post-doctoral position-- ultimately leading to a tenured academic appointment and becoming principle investigator of a lab at a research university. Receiving this F31 NRSA Fellowship will be a significant step towards my future success.